Researchers at Washington State University (WSU) have used disposable masks to improve the strength of concrete by as much as 47 percent, the WSU university press release explained.
As the coronavirus pandemic continues, so does the use of disposable masks that often find themselves littered not only in public places but also in our oceans. Last year, a study estimated that mask pollution rose by a whopping 9,000 percent as countries imposed mask mandates to rein in the spread of the virus. However, the billions of masks produced during this period have become a massive challenge for waste management.
What are disposable masks made of?
Disposable surgical masks can be made of polyester fabric or polystyrene, polyethylene or polypropylene — thermoplastic polymers that can be set into most shapes while working at high temperatures. The myriad filters seen in N95 masks also use polypropylene and when left untreated can remain in the environment for decades. Apart from the polymer, masks also contain metal clips and cotton loops, which although recyclable, end up in heaps of untreated waste.
However, if they are processed properly, used masks can be a valuable commodity as Professor Xianming Shi from the Department of Civil and Environmental Engineering at WSU successfully discovered when he experimented and found a use for masks in concrete.
This may be very beneficial to our environment, as, our regular readers will be well aware, concrete production is a carbon-intensive exercise and is responsible for as much as eight percent of global emissions.
Other experiments to reduce carbon emissions have found that the addition of microfibers increases the strength of cement, thereby reducing its requirement for a project and utlimately reducing emissions. That said, microfibers are an expensive input in construction, which can block them from being widely used.
Adding disposable masks to the mix
As an alternative, Prof. Shi and his team turned to disposed face masks and developed a process to turn them into microfibers to be used in concrete production. By cutting the masks into five to 30 mm-long pieces and treating them with graphene oxide before mixing them in the cement paste, the researchers managed to absorb or dissipate the fracture energy that usually contributes to tiny cracks in concrete.
The graphene oxide allows the microfibers to adhere strongly to the surface without which tiny gaps could occur, which could turn into larger cracks and the material's eventual failure.
The researchers also repurposed the cotton loops and metal clips from the face masks by shredding them and adding them to ordinary Portland cement, the basic ingredient for any concrete, grout, or mortar products.
Their proof of concept study showed that the concrete made using mask materials was 47 percent stronger after a month of curing. The team is now working to determine if the concrete is protected from frost damage and the persistent use of deicers on roadways. In the future, the technique could be applied to use other polymers such as discarded clothing, which would serve as an incentive to the collection of this waste.
The findings of the study were published in Materials Letters.
Used face masks resulting from the COVID-19 pandemic are forming a new waste stream that poses a considerable environmental risk to the ecosystem if not properly disposed of. This work explored an environmentally friendly solution to diverting such waste to a value-added application, i.e., fabricating waste mask microfibers for use in cementitious composites. To improve the interfacial transition zone between mask fibers and cement paste matrix, the microfibers made from recycled medical masks are pre-treated in an aqueous solution of graphene oxide (GO, at 0.05 wt%). In a cement paste with the water/cement ratio of 0.40, the GO-treated mask fibers admixed at 0.1 vol% showed great potential for improving the splitting tensile strength (by 47% at 28 days), even though they slightly decreased the compressive strength of the paste (by 3% at 28 days). Microscopic investigation was also carried out to reveal the enhancement mechanism of GO-treated fibers. This study preliminarily demonstrated the feasibility to upcycle waste masks in the concrete industry and provided a new strategy for disposing of waste masks.